Change in the Chemical Composition and Strength of Wood that has been Used for a Long Time Under Water

The article shows the importance of analyzing old wood strength properties in restoration and monitoring the structure's condition. The issue of the characteristics of wooden structures destruction in the salty water of the Gulf of Finland is discussed. In particular, wood's physical and mechanical properties are analyzed during the long-term operation in water. The result of testing of small standard samples for different types of stress states is shown. Changes in the chemical composition of wood are identified. The change in the chemical composition of the material affecting its strength properties is described on the example of Fort Kronschlot crib foundation. It has been established that the process of diffusion, amplified by alternating wave loads, led to the washing of extractive substances, a decrease in potassium, and a lack of calcium in the cell walls of tracheids. The results of this research work may be useful in assessing the residual life of long-term wooden structures underwater and in predicting the restoration time for these structures more accurately.